The invention relates to an electromotor which is mounted in a housing having two axial ends which are closed by means of axial end shields. The stator and rotor of the electromotor are sealingly mounted in the housing and the rotor is rotatably mounted in the region of one of the axial end shields. A motor shaft supports the rotor and extends through one of the axial end shields of the motor housing. An air impeller wheel is rotatably secured on the motor shaft and serves to impel cooling air. This impeller has an exterior shielding made out of non-electrically conducting material, in which the impeller wheel is housed. This outer shield defines through-stream passages for cooling air and this outer shield surrounds the motor housing for purposes of air cooling it. This shield includes a cladding made of non-electrically conducting material and covers the drive end of the motor shaft. The electromotor of the invention is particularly suitable for driving a barrel or container pump.
Electromotors of this type are generally known. They find application, for example, as drive motors for barrel pumps, hand stirrers or similar arrangements, during the operation of which the handling of the motor is generally necessary by a person servicing the device is generally necessary. In such an arrangement it is accordingly essential that appropriate protection be provided against electric shocks which might be imparted to a person contacting the motor. Depending on the type of protection rendered, such motors are classified in West Germany according to "DIN-Norms" which specifies the degree of protection they afford.
Thus certain electromotors according to one of these types require a conductor which assures that, when a contact occurs between certain parts of the motor, an electrically conducting circuit is formed with certain parts of the motor housing, and electrical charge which appears is grounded by means of the conductor, so that such a contact does not lead to a risk of electric shock for the user of the electromotor. With motors affording a different electrical insulation protection, the requirement must, on the other hand, be met that no such electrically insulated members are to be installed because of the point of view that electric charges to the housing parts can also be imparted via such insulated conductors without electrically conducting connections appearing between the inner conductors of the motor and the housing. The application of such electrical charges to the housing has in particular the drawback that, if such a motor is to operate in an explosion-endangered space, for example in a space that holds explosive gases, operating conditions may cause sparking engendered by sudden break-off or tear-off or snapping of parts which could cause an explosion. Therefore, the requirements of the last mentioned class of motors require that, also with a connection of electrically conducting parts with any kind of metallic motor parts, the housing parts which are subject to being touched hold no electric charge. Moreover, with devices of this class of housing there must also be insured that no electrostatic charge is present, such as, for example, an electric charge that may build up during the friction caused by cleaning the present.
There is disclosed in West German patent application No. 30 12 715 an explosion-protected electromotor with a pressure-secured encapsuled metallic housing. This motor housing is provided with a double protective insulation whereby all contactable, respectively externally facing metallic parts, have an insulation which is provided in addition to the conventional insulations. This additional insulation takes the form of an inner cladding of the motor housing formed by an insulating synthetic coating and a corresponding cladding of the motor shaft, as well as a shielding of the shaft-through-passages by means of the air impeller wheel being made out of synthetic material which is mounted on the motor shaft. The electrical connection means and switch housing are also clad in a similar manner as the insulating motor housing in their interior sides with insulating synthetic material coatings in a pressure-proof manner.
With the aforedescribed known electromotor, it is assured that the auxiliary insulation in the form of synthetic coatings are not damaged, so that parts contacted by the person servicing the device are not electrically charged. However, it has been found problematic to provide on the one hand the rather cumbersome construction for such an electromotor and, on the other hand, to overcome the problems concerning heat conduction, towards the exterior which arise due to the inner cladding of the housing being made of synthetic material.
It is known from West German patent application No. 35 14 685 to provide an electromotor which is mounted within a housing made of synthetic material which has a dividing cross-sectional member. The housing encloses the motor at a predetermined distance and has end caps which define, in the region of these caps, through flow openings providing passage for cooling air. The cooling air is transported by an impeller wheel which, on the side opposite to the drive side of the motor, is arranged outside the motor housing proper but nevertheless within the housing made of synthetic material. The motor is mounted within the synthetic material housing in such a way that an air gap is formed for conduction of the cooling air, which gap surrounds the motor.
The motor disclosed in the aforementioned West German published publication No. 35 14 685 is a so-called "trunk-motor" with exterior air cooling, which is adapted for driving a cement mixer or the like but is not suitable as a drive motor for arrangements wherein an explosion-endangered environment exists or for transporting fluids which produce explosive vapors.
Such a known motor is particularly unsuitable as drive means for a barrel or container pump.